Summary: Astronomy & Astrophysics manuscript no. Gk111 December 14, 2004
(DOI: will be inserted by hand later)
The Effect of Metastable Level Populations on the Ionization
Fraction of Li≠like ions
J.G. Doyle 1 , H.P. Summers 2 and P. Bryans 2
1 Armagh Observatory, College Hill, Armagh, BT61 9DG, N. Ireland
2 Department of Physics, University of Strathclyde, Glasgow, Scotland
Received date, accepted date
Abstract. Lines from Li≠like ions have been known to produce theoretical intensities under≠estimated compared to lines of a
similar formation temperature. Here we investigate this anomalous behaviour whereby the ionization fractions are calculated
using the ADAS code considering the electron density dependence of dielectronic recombination coupled with collisional
ionization from metastable levels. For the lines investigated, the line contribution functions show a clear dependence with
increasing electron density. For example, C ## 1548 Ň shows over a factor of three enhancement for N e = 10 12 cm -3 . The
increase in the higher temperature lines is lower, but are still in the range of 30 to 60%. Furthermore, all the lines have their
peak contribution shifted to lower temperature. Calculating the total radiative power output at an electron density of 10 11 cm -3 ,
we find that the di#erence in the transition region is 10--15% while above 10 6 K the di#erence is around 30% compared to the
low density value.
Key words. Sun: atmosphere -- Di≠electronic Recombination -- metastable levels -- contributon function -- electron density --
line intensity -- UV/EUV radiation
1. Introduction